1. Field of the Invention
The present invention relates to a phase angle controller for controlling a phase angle between two rotary members. Particularly, the present invention is concerned with a phase changing device having a wide control range for realizing an optimum control position in a valve timing controller (hereinafter referred to as “VTC”) for an internal combustion engine which device makes variable an opening/closing timing of an intake valve or an exhaust valve actuated by an crank shaft through a cam shaft.
2. Description of the Related Art
First, a VTC used in an automobile engine will be outlined with reference to FIG. 16. In a four-stroke engine, sprockets mounted on front ends of cam shafts for intake and exhaust are rotated through a timing belt with rotation of a crank shaft. At this time, the cam shaft speed is reduced by half in accordance with a gear ratio. A VTC is mounted between each cam shaft and the associated sprocket to change a relative rotational position between the two. The VTC has a function of changing a rotational phase of the cam shaft relative to the crank shaft and thereby change the opening/closing timing of an intake or exhaust valve.
Functions or effects attained by each VTC described above will be explained below with reference to FIG. 17. In FIG. 17 there are shown effects obtained by changing the opening/closing phase of the intake valve in accordance with various operating conditions with use of the intake-side VTC.
In FIG. 17, “a.” shows an optimum intake valve opening/closing phase in an idling condition just after starting of an engine. By shifting the intake valve timing to an advance side relative to a top-stage base position in FIG. 17, the intake valve is opened quickly and residual unburned HC (hydrocarbon) gas is introduced and re-burned. Moreover, by setting long an overlapping period between the exhaust stroke and the intake stroke to promote the vaporization of newly supplied fuel, it is possible to decrease the amount of HC contained in the exhaust gas.
In FIG. 17, “b.” shows an optimum intake valve opening/closing phase in an idling condition after the end of warming-up. In this case, by shifting the intake valve timing to a delay side relative to the base position, it is possible to delay the close timing of the intake valve and thereby decrease the amount of intake air. Therefore, by throttling a throttle valve it is possible to suppress a pump loss and decrease the amount of fuel consumed.
In FIG. 17, “c.” shows intake valve opening/closing phases optimum for increasing the engine torque in a high load condition. As to increasing the engine torque, the way of using VTC is different between the case where the engine is operating at low speed and the case where the engine is operating at high speed. In a low-speed operation of the engine, the amount of intake air becomes maximum when the intake valve is closed in the vicinity of a bottom dead center position of a piston in which a geometric volume within a cylinder becomes maximum, and therefore the phase is shifted to the advance side relative to the base position. In a high-speed operation of the engine, since the amount of intake air is to be increased by utilizing an inertial supercharging effect, the phase is shifted to the delay side relative to the base position to delay the close timing of the intake valve. Thus, the way of use of the VTC differs depending on the engine speed, but the mass of intake air can be increased at any rotational speed by the VTC, thus making combustion of a larger amount of fuel possible and thereby permitting an increase of the engine torque.
In various operating conditions of the valve timing controller, in both idling of “b.” and high-speed operation of “c.”, the intake valve timing is shifted to the delay side relative to the base position in the top stage to attain the effects shown in FIG. 17. It can be said that the base position is a fixed valve timing of an engine not equipped with VTC. In this case, it is also a valve timing able to start the engine. Therefore, in a conventional intake VTC wherein a locked position at the time of starting is a most delayed position in a control range, the base position lies near the most delayed position and it is impossible to make a further phase conversion to the delay side.
Further, locking the VTC irrespective of position thereof at the time of start-up of the engine has heretofore been required because the VTC is unstable until ensuring a predetermined oil pressure after engine starting and there is a possibility that a beating noise may occur due to vibration or collision.
In view of this point there has heretofore been proposed an intermediate position locking mechanism in a VTC wherein a locked position in engine starting is set at an intermediate position (see, for example, Japanese Patent Laid-Open Publication No. 2001-241307). This intermediate position locking mechanism is based on the way of thinking that in connection with locking to the intermediate position by a vane-induced oil pressure, a stopper portion is formed only at the time of engine stop and starting during automatic return from an advance side to a most delayed position and a locking mechanism such as a locking pin is operated while the VTC is held temporarily on the stopper portion. In Japanese Patent Laid-Open Publication No. Hei 11(1999)-343819 is proposed an intermediate position locking mechanism wherein an automatic return to an intermediate locking position is to be made from not only an advance side but also a delay side.